getting CPU usage in macosx

gistfile1.c

#include <sys/sysctl.h>
#include <sys/types.h>
#include <mach/mach.h>
#include <mach/processor_info.h>
#include <mach/mach_host.h>

processor_info_array_t cpuInfo, prevCpuInfo;
mach_msg_type_number_t numCpuInfo, numPrevCpuInfo;
unsigned numCPUs;



int mib[2U] = { CTL_HW, HW_NCPU };
size_t sizeOfNumCPUs = sizeof(numCPUs);
int status = sysctl(mib, 2U, &numCPUs, &sizeOfNumCPUs, NULL, 0U);
if(status)
    numCPUs = 1;

// in a timed loop

natural_t numCPUsU = 0U;
kern_return_t err = host_processor_info(mach_host_self(), PROCESSOR_CPU_LOAD_INFO, &numCPUsU, &cpuInfo, &numCpuInfo);
if(err == KERN_SUCCESS) {
  for(unsigned i = 0U; i < numCPUs; ++i) {
        float inUse, total;
        if(prevCpuInfo) {
                inUse = (
                         (cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_USER]   - prevCpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_USER])
                         + (cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_SYSTEM] - prevCpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_SYSTEM])
                         + (cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_NICE]   - prevCpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_NICE])
                         );
                total = inUse + (cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_IDLE] - prevCpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_IDLE]);
        } else {
                inUse = cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_USER] + cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_SYSTEM] + cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_NICE];
                total = inUse + cpuInfo[(CPU_STATE_MAX * i) + CPU_STATE_IDLE];
        }

        NSLog(@"Core: %u Usage: %f",i,inUse / total);
    }
    if(prevCpuInfo) {
            size_t prevCpuInfoSize = sizeof(integer_t) * numPrevCpuInfo;
            vm_deallocate(mach_task_self(), (vm_address_t)prevCpuInfo, prevCpuInfoSize);
    }

    prevCpuInfo = cpuInfo;
    numPrevCpuInfo = numCpuInfo;

    cpuInfo = NULL;
    numCpuInfo = 0U;
} else {
    // error 
}

extracted from http://stackoverflow.com/questions/6785069/get-cpu-percent-usage?lq=1